Due to excellent magnetic properties and economy, rare earth permanent magnets are on widespread use in the field of electric and electronic equipment. In these years there is an increasing demand for them, with further enhancement of their properties being desired. Of the rare earth permanent magnets, R—Fe—B base rare earth permanent magnets are quite excellent permanent magnet materials, as compared with rare earth-cobalt base magnets, in that Nd which is one of predominant elements is richer in resource than Sm, and their magnetic properties surpass those of rare earth-cobalt base magnets. They are also advantageous in economy in that the majority is constituted by inexpensive Fe.
The R—Fe—B base permanent magnets, however, have problems that (1) the magnets themselves are liable to rust due to high iron contents and require certain surface treatment and (2) their use in a high-temperature environment is difficult due to a low Curie point.
Heretofore, for achieving further improvements in magnetic properties of R—Fe—B base permanent magnets and alleviating the above problems, attempts have been made to add a variety of elements thereto. For instance, there were proposed magnet materials having Ti, Ni, Bi, V or the like added for providing stable coercive force (see JP-A 59-64733 and JP-A 59-132104); magnet materials having Te, Zn, Se or the like added for improving coercive force (see JP-A 60-176203); magnet materials having 0.02 to 0.5 at % of Cu added for optimizing heat treatment conditions (see JP-A 1-219143); magnet materials in which Fe is substituted with Co and Ni in a high concentration for improving corrosion resistance (see Japanese Patent No. 2,675,430); and magnet materials having rare earth oxide R′mOn (wherein R′ is Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu) added thereto for reducing the cost and improving coercive force and resistivity (see JP-A 11-251125).
Gasifiable elements such as oxygen and carbon are generally considered as impurities to be excluded because they are believed to consume excess rare earth elements localized in the grain boundary phase and thus detract from magnetic properties. For this reason, several proposals have been made for minimizing the contamination of such gas impurities, including the method to prevent the magnet alloy or powder from these elements during the manufacturing process, to use the high purity raw materials, and the method of removing the impurity elements entrained with the raw materials out of the system.